Levels are used by carpenters, masons, drywallers and the like for helping to assure that surfaces are horizontal, vertical, or at a specified angular relationship to the horizon. A typical level includes at least two vials, one each for ascertaining whether a surface is “level,” i.e., horizontal, or “plumb,” i.e., vertical.
A level vial comprises a tube made of clear glass or, preferably, clear plastic (acrylic, for example), the barrel-shaped cavity of which is partially filled with a liquid such as mineral spirits. The vial is not completely filled and a bubble is thereby formed when the vial is closed. Typically, two marker rings are applied to the outside of the vial in positions to visually divide the cavity into three portions of about equal length. Level and plumb conditions are ascertained by noting the position of the bubble with respect to the marker rings.
A problem with molding substantially-finished vials is that acrylic, the material predominantly used for making molded vials, does not stretch well. If one attempts manufacture of an acrylic vial which has thick walls (for breakage resistance), the stretch-resisting characteristic of acrylic causes breakage of core pins used in the injection molding process. On the other hand, a thin-wall vial is much more subject to breakage—builder's levels often receiving rough treatment in use.
One known method of avoiding core pin breakage while providing a vial of satisfactory thickness with marker rings is to machine a barrel-shaped inner cavity in a preform. Inner grooves are machined in the inner surface to receive C-shaped rings like common snap rings. Such rings necessarily have a discontinuity or opening about the perimeter so that the ring can be compressed radially for insertion into the cavity. A ring is seated in each of two respective grooves.
A problem with such construction is that the surface transition between the C-shaped ring and the inner wall of the tube will not be smooth, at least because of the existence of a small annular space (at the chamfer) between the ring and the wall. In other words, a slight edge will be presented to a bubble moving along the vial and such edge may cause the bubble to “hang up” in its travel and yield an inaccurate reading. Furthermore, positioning of the marker rings in the grooves is often not exact and often results in imprecise readings.
Another problem with known level vials involves exteriorly-applied marker rings. Since such rings are at least somewhat exposed to contact by foreign objects, portions of such rings can be worn or chipped away over time.
An improved level vial which has a sturdy, breakage-resistant wall, which permits the vial bubble to move smoothly and freely along the vial cavity would be an important advance in the art. Furthermore, such a vial which provides a single-material cavity surface would significantly improve upon the prior art. Finally, an improved vial comprising a machined cylinder with a sleeve molded thereon would solve these noted problems in the prior art.